Systems and methods for plasma jets

ABSTRACT

A plasma jet system includes a housing with an opening. A plasma generator is coupled to ionize a fluid in the housing. An electromagnetic accelerator is coupled to generate an electric field that accelerates ionized fluid in the housing toward the opening. A controller can modulate the frequency of the electric field to cause the ionized fluid to form a plasma vortex flow through the opening. A magnetic field is applied normal to the direction of the plasma vortex flow to mitigate the momentum of the electrons. The electrons slowed by the magnetic field can be collected and conducted to a location where they are re-inserted into the plasma vortex flow to maintain charge neutrality.

BACKGROUND

Active flow control involves modification of the turbulent structure ofeddies in most complex flows with the intent to improve aerodynamicperformance of air vehicle flight control and propulsion systems. Suchcapability can increase range and maneuverability, reduce acousticloads, signature, weight, and cost. In some systems, a relatively smallamount of high-momentum secondary fluid is used to enhance the naturallyoccurring instabilities of the main flow. For example, it is known touse active flow control in applications such as favorably influencingthe flow over an aerodynamic surface, heating/cooling components,vectoring a primary fluid flow, and mixing fluids.

One type of device that can be used for active flow control in subsonicsystems is referred to as a zero-net-mass jet. A typical zero-net-massjet actuator comprises a housing defining an internal chamber. Anorifice is present in a wall of the housing. The actuator furtherincludes a mechanism in or about the housing for periodically changingthe volume within the internal chamber so that a series of fluidvortices are generated and projected in an external environment out fromthe orifice of the housing. Various volume changing mechanisms areknown, for example a piston positioned in the jet housing to move sothat fluid is moved in and out of the orifice during reciprocation ofthe piston, or a flexible diaphragm as a wall of the housing. Theflexible diaphragm is typically actuated by a piezoelectric actuator orother appropriate means.

Typically, a control system is utilized to create time-harmonic motionof the diaphragm. As the diaphragm moves into the chamber, decreasingthe chamber volume, fluid is intermittently ejected from the chamberthrough the orifice. As a quantity of fluid passes through the orifice,the flow separates at the sharp edges of the orifice and creates a shearlayer, which rolls up into a vortex sheet or ring. As each intermittentquantity of fluid is emitted, a separate vortical structure is generatedcreating a train of vortices moving away from the orifice. Thesevortices move away from the edges of the orifice under their ownself-induced velocity. As the diaphragm moves outward with respect tothe chamber, increasing the chamber volume, ambient fluid is drawn fromall directions around the orifice into the chamber. Since the vorticesare already removed from the edges of the orifice, they are not affectedby the ambient fluid being entrained into the chamber. As the vorticestravel away from the orifice, they synthesize a jet of fluid, a“zero-net-mass jet,” through entrainment of the ambient fluid.

However, piezoelectric diaphragms used to form zero-net-mass jets aregenerally unreliable due to moving parts and cause vibration in devicesin which they are installed. Further, the amplitude, temperature, andfrequency at which the diaphragms can operate is limited, with theresult that piezoelectrically-driven zero-net-mass jets generate limitedjet velocity and have little practical application in flows aboveapproximately Mach 0.3.

In physics and chemistry, plasma (also called an ionized gas) is anenergetic state of matter in which some or all of the electrons in theouter atomic orbital rings have become separated from the atom.Excitation of a plasma requires partial ionization of neutral atomsand/or molecules of a medium. There are several ways to cause ionizationincluding collisions of energetic particles, strong electric fields, andionizing radiation. The energy for ionization may come from the heat ofchemical or nuclear reactions of the medium, as in flames, for instance.Alternatively, already released charged particles may be accelerated byelectric fields, generated electromagnetically or by radiation fields.

There are two broad categories of plasma, hot plasmas and cold plasmas.In a hot plasma, full ionization takes place, and the ions and theelectrons are in thermal equilibrium. A cold plasma (also known as aweakly ionized plasma) is one where only a small fraction of the atomsin a gas are ionized, and the electrons reach a very high temperature,whereas the ions remain at the ambient temperature. These plasmas can becreated by using a high electric field, or through electron bombardmentfrom an electron gun, and other means . . .

SUMMARY

In some embodiments, a plasma jet system is disclosed that includes ahousing with an opening. A plasma generator is coupled to ionize a fluidin the housing. An electromagnetic accelerator is coupled to generate anelectric field that accelerates ionized fluid in the housing toward theopening. A controller can modulate the frequency of the electric fieldto cause the ionized fluid to form a plasma vortex flow through theopening. A magnetic field is applied normal to the direction of theplasma vortex flow to mitigate the momentum of the electrons. Theelectrons slowed by the magnetic field can be collected and conducted toa location where they are re-inserted into the plasma vortex flow tomaintain charge neutrality. The plasma jet system has no moving partsand no change in mass flow volume is required to create the plasma flow.

The foregoing has outlined rather broadly the features and technicaladvantages of embodiments of the present invention so that those skilledin the art may better understand the detailed description of embodimentsof the invention that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments disclosed herein may be better understood, and theirnumerous objects, features, and advantages made apparent to thoseskilled in the art by referencing the accompanying drawings. The use ofthe same reference symbols in different drawings indicates similar oridentical items.

FIG. 1 is a diagram of an embodiment of a plasma jet system;

FIGS. 2A and 2B show diagrams of another embodiment of a plasma jetsystem;

FIGS. 3A and 3B show diagrams of another embodiment of a plasma jetsystem;

FIG. 3C shows pairs of electrodes that can be activated and deactivatedin series to generate an electric field to accelerate the plasma;

FIG. 4 is a diagram of another embodiment of a plasma jet system;

FIG. 5 is a diagram of an embodiment of a plasma injector;

FIG. 6 is a diagram of an embodiment of a plasma jet system;

FIG. 7A shows an embodiment of engine configured with plasma jets tovector fluid flow at the throat and/or exit areas of a nozzle;

FIG. 7B shows an embodiment of engine configured with a duct to collecthigh-pressure air from flow at compressor section and provide thehigh-pressure flow to plasma jets;

FIG. 8 shows an embodiment of a nozzle with plasma jets located toreduce the effective cross sectional area of nozzle throat;

FIG. 9, an embodiment of nozzle is shown including thrust vectoring withplasma jets;

FIG. 10 shows an embodiment of aircraft with plasma jets embedded inwings;

FIGS. 11 and 12 shows an embodiment of an aerodynamic surface withplasma jets that are configured to change the effective aerodynamicshape of the surface; and

FIG. 13 is a perspective view of an embodiment of self-propelled rotorin which a plasma jet can be utilized.

DETAILED DESCRIPTION OF THE DRAWINGS

What is desired is a fixed-volume zero-net-mass jet actuator withsufficient momentum and control authority that can be used to activelycontrol high velocity flows in a variety of applications, such asengines, aerodynamic surfaces, mixing, and heating and cooling.Embodiments disclosed herein provide a plasma flow accelerated throughan electric field to create a high speed, steady and/or high frequencypulsed plasma jet. The plasma jet can be configured to control flowwithout diverting a portion of the primary flow or requiring anauxiliary flow source.

FIG. 1 shows a diagram of components that can be included in someembodiments of plasma jet system 100, including controller 102 coupledto operate plasma generator 104 and electromagnetic accelerator 106.Plasma generator 104 can be configured to generate plasma in housing109. Cavity 110 in housing 109 is formed with at least one opening.Electromagnetic accelerator 106 can be configured to generate anelectric field E and a magnetic field B. The electric field Eaccelerates the plasma within cavity 110 toward an opening in housing109, while the electrons (indicated by “−” symbols) are accelerated inthe opposite direction. Controller 102 modulates the frequency of theelectric field E to cause ionized fluid (indicated by “+” symbols) toform a pulsed plasma vortex flow 112 through the opening.

The magnetic field B is applied normal to the direction of the plasmajet and creates a large force on the electrons. The force of magneticfield B mitigates the momentum of the electrons, which aids collectionof the electrons by positive electrical terminal 114, such as a cathode.Positive terminal 114 can be coupled to a conductive element 116 andconfigured to transport the electrons to a location downstream of plasmavortex flow 112. A negative terminal 118 such as an anode can be coupledto the other end of conductive element 116 at a downstream location,where the electrons can be re-inserted into plasma vortex flow 112 tohelp neutralize the charge of flow 112. A switch 120 can be coupledbetween conductive element 118 and controller 102. Controller 102 can beconfigured to receive information from one or more sensor(s) 122regarding the characteristics of flow 112 at some downstream location,and control operation of plasma generator 104 and electromagneticaccelerator 106.

Controller 102 can operate electromagnetic accelerator 106 to provide asteady or a pulsed electric field. When a pulsed electric field isapplied, a series of plasma vortices issue from an opening in cavity110, shown as plasma vortex flow 112. The strength and/or the pulsefrequency of the electric field can be varied, depending on the forcerequired from plasma vortex flow 112.

Controller 102 is typically implemented with a processing system thatcan be embodied in any suitable computing device(s) using any suitablecombination of firmware, software, and/or hardware, such asmicroprocessors, Field Programmable Gate Arrays (FPGAs), ApplicationSpecific Integrated Circuit (ASICs), or other suitable devices.Controller 102 can be coupled to a power supply (not shown) to controlpower supplied to plasma generator 104 and electromagnetic accelerator106. Sensor(s) 122 can also provide information regarding the velocity,pressure, temperature, and other characteristics of flow 112 tocontroller 102 to operate electromagnetic accelerator 106 and plasmagenerator 104.

Any suitable component or combination of components can be used forcontroller 102, plasma generator 104, electromagnetic accelerator 106,positive terminal 114, negative terminal 118, conductor 116, andsensor(s) 122. For example, plasma generator 104 can be implemented bystrong electric fields, electron beams, microwaves, and other phenomenaand/or components capable of generating plasma. Electromagneticaccelerator 106 can be implemented with one or more suitable device(s)capable of generating an electrical field transverse to a magneticfield.

FIGS. 2A and 2B show perspective and side cut-away views, respectively,of an embodiment of another plasma jet system 200 configured to generatea continuous plasma jet 202. Controller 102 is coupled to regulateelectrodes 204 to generate an electric field that accelerates flow 206to form plasma jet 202. Electrodes 204 may be pulsed at one or moredesired frequencies, and/or operated to apply a continuous electricfield. The functions of plasma generator 104 (FIG. 1) can be performedby electron beams 208 being injected into cavity 110 of housing 209through electron beam windows 210 to ionize flow 206. Windows 210 may beheated by electron beams 208, and are of sufficient mechanical strengthfor the environment in which housing 209 is utilized. Any suitable typeof window 210 can be utilized. For example, in some configurations, thinmetallic foils with passive cooling can be utilized for windows 210. Inother configurations with electron beams 208 of relatively high currentdensities, either active cooling or plasma windows can be utilized.Windows 210 typically comprise only a portion of one or more walls ofhousing 209. For example, FIGS. 2A and 2B shows windows 210 as a seriesof rectangular strips in opposing sidewalls, however any suitablenumber, shape, and configuration of windows 210 can be used. The amountof plasma generated can also be varied, as required, by controllinggeneration of electron beams 208.

Housing 209 can be configured with one or more magnet devices 212 thatcan be operated by controller 102 to create a transverse magnetic fieldnormal to the direction of the electric field. Electrodes 204 and magnetdevices 212 together perform at least some of the functions ofelectromagnetic field generator 106 (FIG. 1). Magnetic devices 212 suchas permanent magnets, electromagnets, and/or superconducting magnets canbe used to generate a magnetic field that is aligned approximatelynormal to the electric field E and flow 206. Other suitable devices forgenerating a magnetic field can be used, in addition to, or instead of,magnet devices 212. Additionally, although magnet devices 212 are showndistributed over the length of housing 209, one or more magnet devices212 can be positioned in any one or more suitable locations relative tohousing 209 or portions of housing 209.

Housing 209 is open at both ends to allow flow 206 to enter one end andplasma jet 202 to exit the other end. Flow 206 can be any suitableliquid, gaseous, and/or solid substance(s) supplied from any suitablesource (s). For example, flow 206 can be supplied from a secondary orauxiliary source such as a tank of compressed gas or fluid (not shown).Flow 206 can also be supplied by diverting a portion of a primary flowin addition to, or instead of, being supplied from a secondary source.Electron beams 208 can increase the ionization of flow 206, which can besupplied as a non-ionized, partially ionized, or fully ionizedsubstance, as required.

FIGS. 3A and 3B show perspective and side cut-away views, respectively,of an embodiment of plasma jet system 300 that is similar to plasma jetsystem 200 (FIGS. 2A and 2B), except housing 302 includes a closed end304, and an open end through which flow 306 enters, and plasma vortexflow 112 exits. Plasma jet system 300 is referred to as a zero-net-masssystem because flow 306 is drawn in by reduced pressure created inhousing 302 by the flow of plasma vortex flow 112 out of housing 302.

Referring to FIGS. 3A and 3C, electrodes 310 can be arranged inelectrode pairs with alternating polarity. Controller 102 can activateand deactivate each pair of electrodes 310 in series over a period oftime. For example, at time T1, a first pair of electrodes 310 isactivated. At time T2, the first pair of electrodes 310 is deactivatedand the second pair of electrodes 310 is activated. At time T3, thesecond pair of electrodes 310 is deactivated and the third pair ofelectrodes 310 is activated, and so on. When the last pair of electrodes310 is deactivated, the first pair can be activated to begin the seriesover again, causing a wave of pulsing electric field E to “travel”through housing 302. Such an arrangement of electrodes 310 can be usedin various embodiments of plasma jet systems, including systems 100(FIG. 1), 200 (FIG. 2), and 400 (FIG. 4), as well as system 300.

FIG. 4 shows an embodiment of another plasma jet system 400 configuredwith electrodes 402, 404 of opposing polarity positioned within cavity406 at either end of housing 408. Controller 102 is configured to outputpulsed driver signals to electrodes 402, 404 to create the electricfield that accelerates the ionized fluid into a jet of plasma vortexflow 112. Further, one or more electrodes 402 can also be used togenerate the plasma or ionized flow 410. Additional electrodes 402, 404can be used to accelerate plasma. Note that any suitable device(s) forgenerating an electric field can be used, in addition to, or instead of,electrodes 204. Magnetic field generators 412 are shown near the top andbottom of housing 408 to attract electrons, however, magnetic fieldgenerators 412 can be positioned in any suitable location relative tohousing 408.

Note that various embodiments of plasma jet systems 100 (FIG. 1), 200(FIG. 2), 300 (FIG. 3), and 400 (FIG. 4) do not require movingmechanical components to create a jet of plasma vortex flow 112.Electromagnetic accelerator 106 can be pulsed at frequencies above thosethat can be achieved with mechanical components in other types ofzero-net-mass jets. Additionally, the strength of the electric field Ein cavity 110, and the ionization of flow 206, 306, can be adjusted toachieve plasma vortex flow 112 with much higher velocity thanzero-net-mass jets generated by mechanical systems. Plasma jet systems100, 200, 300, 400 can be configured with components that can withstandvery high speeds and temperatures. Accordingly, plasma vortex flow 112can be generated to control flow at hypersonic temperatures and speeds,as well as lower temperatures and speeds.

The ability to manipulate and control fluid flows with plasma jetsystems has tremendous potential for improving system performance indiverse technological applications, including: mixing and combustionprocesses, boundary layer flow of aerodynamic surfaces, pressure shockstabilization, engine inlet boundary layer diversion, inlet ductsecondary flow control, and thrust management, among others. Shear flowis typically receptive to small disturbances within a limited frequencyband and, as a result, these disturbances are rapidly amplified and leadto substantial modification of the primary flow and the performance ofthe system in which it is employed.

Referring to FIG. 5, an embodiment of a pulsed plasma injector 500 isshown including a high-velocity plasma jet 502 pulsed through a primarynozzle 504 contained within shroud 506. The mixing between plasma jet502 and secondary fluid 508 is a viscous process that tends to dissipateenergy. Pulsing plasma jet 502 reduces the dissipative effects of themixing between plasma jet 502 and secondary fluid 508. Additionally, bypulsing plasma jet 502, a billow 510 of plasma generates one or moreacoustic waves 512 in the downstream flow. Acoustic waves 512 comprisesan elastic interaction with secondary fluid 508 in addition to a mixingphenomenon, achieving a more efficient transfer of energy from plasmajet 502 to secondary fluid 508. Note that controller 102, plasmagenerator 104 and electromagnetic accelerator 106 (FIG. 1) can beincluded in pulsed plasma injector 500 to vary the frequency, duty cycleand amplitude of plasma jet 502 in order to control the efficiency ofsystem 600.

Another embodiment of a plasma jet system 600 is shown in FIG. 6,including a high-pressure plasma source 602 contained within an innernozzle 604. Shroud 606 includes a convergent portion 608 followed by anozzle portion 610 with an opening at exit end 612. In some embodiments,nozzle portion 610 can be divergent, convergent, have a substantiallyconstant cross-section, or a combination of shapes. The geometry ofconvergent portion 608 and nozzle portion 610 can be determined byproperties of the primary flow and secondary fluid. The ratio of across-sectional area of inner nozzle 604 to cross-sectional area ofshroud 606 can be selected so that said primary flow dissipates withinthe boundaries of shroud 606.

In the embodiment shown, inner nozzle 604 is positioned in convergentportion 608 of shroud 606. Plasma vortex flow 614 forms a primary flowthat mixes with a secondary fluid in nozzle portion 610. The efficiencyof the mixing is affected by several variables such as the pulsingfrequency and amplitude of plasma vortex flow 614, and the length andcross-sectional geometry of nozzle portion 610. In some embodiments, thelength of nozzle portion 610 can be based on a harmonic of the frequencyof plasma vortex flow 614.

Plasma jet system 600 can be used in a variety of industrialapplications such as a smokestack, where it may be desirable to direct aplume of a smokestack with ejectors to drive the smoke and exhaust in acertain direction. Plasma jet system 600 can be used to pump additionalmass flow in an engine, or in the ventilation or environmental controlsystem of a machine or vehicle. In some embodiments, plasma jet system600 can boost pumping capacity by 100% or more over a steady-stateejector, essentially doubling the pumped mass flow. Plasma jet system600 can also be used to cool electronic equipment, as well as otherdevices.

In other embodiments, a series of nested plasma jet systems 600 can beincluded to form two or more stages of mixing. In still furtherembodiments, multiple plasma jet systems 600 can be included in the samestage to increase the amount of fluids that are mixed in the stage. Notethat inner nozzle 604 can be configured with an open housing 202 (FIG.2B) or closed housing 302 (FIG. 3B), depending on whether plasma jetsystem 600 is intended to be zero net mass flow or not. Additionally,controller 102, plasma generator 104 and electromagnetic accelerator 106(FIG. 1) can be included in plasma jet system 600 to vary the frequency,duty cycle and amplitude of plasma vortex flow 614 in order to controlthe efficiency of plasma jet system 600.

FIG. 7A shows an embodiment of engine 700 configured with plasma jets702 to vector fluid flow at the throat 704 and/or exit areas 706 ofnozzle 708. As primary flow 710 of air enters jet engine 700 through fansection 712, comprised of a plurality of rotating fan blades, pushesflow 710 into bypass section 714 and compressor section 716. Compressorsection 716 is comprised of a plurality of compressor blades 718, 720which compress flow 710 into combustion chamber 722. Fuel is mixed withflow 710 in combustion chamber 722 and ignited, thereby adding energy toflow 710, increasing the temperature of flow 710 in combustion chamber722. Pressure within combustion chamber 722 forces flow 710 into turbinesection 724, which is comprised of a plurality of turbine blades 726.Turbine section 724 removes some energy from flow 710 to powercompressor section 728 and turbine section 724. Flow 710 then passesinto exhaust chamber 718 where it combines wit the flow from bypasssection 714. An afterburner 730 can provide additional fuel, which canbe ignited to increase the energy of flow 110. Flow 710 is then expelledfrom engine 700 through exit 706 as an exhaust flow.

Engine 700 creates thrust related to the velocity of the mass anddensity of the air of flow 710 over a given time period. Typically, in ajet engine, flow 710 is a subsonic flow of air until it reaches throat704. Nozzle 708 cooperates with exit 706 to accept flow 710 from exhaustchamber 728 and to accelerate exhaust flow 710 to higher velocities,typically supersonic velocities. To achieve optimum acceleration of theexhaust flow, nozzle 708 converges the flow at throat 704, which is thepoint or section in nozzle 708 having the smallest cross sectional area,the constriction of throat 704 typically accelerating flow 710 to asonic velocity, and a supersonic velocity after throat 704. Constrictionof flow 710 at throat 270 operationally translates energy in flow 710from pressure and temperature into velocity, thus creating thrustopposite to the vector of flow 710 as flow 710 exits nozzle 708.Although nozzle 708 is depicted as a fixed geometry nozzle, it should beunderstood that variable geometry nozzles could be incorporated inengine 700 to enhance control of the exhaust flow.

Note that pulsed plasma jets 702 are shown as zero net mass flow jetswith a cavity closed at one end, similar to housing 302 shown in FIG.3B. FIG. 7B shows an embodiment of engine 750 configured with duct 752to collect high-pressure air from flow 710 at compressor section 718 andprovide the high-pressure flow 710 to plasma jets 754. Duct 752 caninclude components to ionize flow 710 as it is delivered to jets 754.Plasma jets 754 can further ionize the flow, if necessary, as the flowis accelerated through a magnetic field and injected into nozzle 708. Amagnetic field may be used to mitigate electron momentum and aid thecollection f electrons by an electrode for reinsertion into the bulkmass flow to maintain charge neutrality of the flow.

In alternative embodiments, duct 752 can collect air from bypass section714, combustion chamber 722 or any other portion of engine 750 havinghigh-pressure air. In an alternative embodiment, a separate compressor(not shown) can provide high-pressure fluid to duct 752. Controller 102controls operation of plasma jets 754, and the flow pressurized fluid induct 752. One or more ducts 752 can be included to provide compressedair to two or more opposing jets 754 located in nozzle 708 and/or otherportions of engine 750.

In both engines 700 and 750, plasma jets 702, 754 can be located atdifferent positions to affect different performance parameters ofengines 700, 750. Additionally, the pulse frequency and amplitude ofplasma jets 702, 754 can be varied to optimize performance. Forinstance, referring to FIG. 8, plasma jets 802 can be located andoperated to reduce the effective cross sectional area of nozzle throat704 to enhance the acceleration of exhaust flow 710 as it exits fromexhaust chamber 728 through exit 706. Controller 102 can direct opposingplasma jets 802 to inject a pulsed secondary flow having mass flow andpulse characteristics adequate to effectively decrease the crosssectional area of throat 704 to not only ensure proper acceleration ofexhaust flow 710, but also to throttle flow 710 to control the pressureand temperature within exhaust chamber 728. If jets 802 inject asecondary flow with similar characteristics, flow 710 can be acceleratedwithout changing its vector (direction) at exit 706.

When engines 700, 750 are operated at varying power settings, the energylevel of flow 710 is varied by, for instance, fluctuation of the amountof fuel in combustion chamber 722. A greater energy level added to flow710 increases the pressure and temperature in exhaust chamber 728.Typically, jet engines 700, 750 increase the cross sectional area of thenozzle when afterburner is selected. At high flow energy levels,controller 102 can direct plasma jets 802 to provide a secondary flowwith decreased blockage of throat 704 to reduce pressure in exhaustchamber 728. When the energy level of flow 710 is maximized by providingfuel into exhaust chamber 728 with afterburner 730, the exhaust flow inexhaust chamber 728 can create an over-pressure which can cause abackflow through turbine section 718 and, in extreme situations, bypasschamber 714. To minimize the effects of the backpressure created inexhaust chamber 728 by initiation of afterburner 730, controller 102 candirect plasma jets 802 to provide no or just minimal blockage of throat704, thus effectively increasing the cross sectional area of throat 704.

Plasma jets 702, 754 can be incorporated into various nozzle designs,including an axisymmetric, rectangular (2-D), elliptical, diamond,triangular shapes, and low observable RADAR and IR configurations.Plasma jets 802 can be formed as one or more slots that encompass all orportion(s) of the periphery of the nozzle 708 to provide a uniform flowalong the entire slot from a single duct, or can include a number ofsmaller injection components within each slot that cooperate to providea uniform flow or a flow that varies along the slot(s).

Referring now to FIG. 9, an embodiment of nozzle 708 is shown includingthrust vectoring features that enhance vehicle maneuverability withoutrequiring complex moving parts or increasing radar or infraredsignatures. One or more plasma jets 802 are oriented to inject asecondary fluid at an angle opposing the direction of primary fluid flow710 to change the direction of the exhaust thrust vector. Nozzle 708accordingly provides a reliable, low cost, highly effective thrustvectoring solution that can be easily implemented with minimaladditional weight.

In some embodiments, exit area 706 is a two-dimensional rectangularnozzle configuration. The thrust-vectoring control moments areproportional to the thrust vector deflection angle and the force exertedby the vectored primary fluid flow 710.

Plasma jets 802 can generate pitch, roll, and yaw control moments bydeflecting the primary flow 710 vertically and horizontally. For singlenozzle configurations, vertical deflections cause pitching moments, andhorizontal deflections cause yawing moments. Multiple nozzles 708 can bepositioned at desired locations relative to the axes of the vehicle sothat vertical deflections cause pitching moments, differential verticaldeflections cause rolling moments, and horizontal deflections causeyawing moments. In some embodiments, plasma jets 802 are disposed onopposing sidewalls. In other embodiments, one or more plasma jets 802can be formed in only one sidewall. Plasma jets 802 can be arranged inrows having the same or a different number of plasma jets 802 in eachrow. Groups of plasma jets 802 can be arranged in nozzle 708 to meet therequirements for a particular use.

While plasma jets 802 can be positioned at various locations onsidewalls of nozzle 708, the greatest amount of thrust vectoring istypically achieved by positioning plasma jets 802 as close to the freestream edge of exit area 706 as possible. The force exerted by plasmajets 802 is also dependent on the diameter and the pressure of plasmavortex flow from plasma jets 802. Plasma jets 802 with larger diametersand lower pressure can achieve the same overall fluid mass flow assmaller diameters with higher pressure secondary fluid flow. Anycombination of number, size, and location of plasma jets 802, and rateof secondary fluid flow, can be configured to provide the desired thrustvectoring capability.

Note that plasma jets 802 can be provided in any number of sidewalls toprovide maneuvering control in the desired directions. Further,secondary flow can be injected simultaneously in two or more sidewallsto effect maneuvering control in two or more directions. It should alsobe noted that the position of one or more of nozzles 708 on a vehiclecan be selected with respect to the vehicle's center of gravity toincrease or decrease the pitch, roll, and yaw moments that can beachieved with a given amount of thrust vectoring force.

The systems depicted in FIGS. 7A–9 can perform or supplement thefunctions of a thrust vectoring, variable geometry nozzle to adjust theeffective operating parameters of a nozzle over a jet engine's fullpower range. Note that although jet engines 700, 750 are used asexamples of how plasma jets 702, 754 can be used to control flow, plasmajets 702, 754 can be used in other types of engines, including plasmaengines, among others.

Plasma jets 802 can also be used in a wide variety of otherapplications, including modifying the shape of aerodynamic surfaces,such as airfoils. FIG. 10 shows an embodiment of aircraft 1000 withplasma jets 802 embedded in wings 1004. The cross-section of wings 1004along the longitudinal axis 1006 of aircraft 1000 form an airfoil 1102,as shown in FIGS. 11 and 12, that is shaped to create a pressuredifference between the upper surface (suction side) and pressureincrease on the lower surface (pressure surface) to produce a liftingforce. Airfoils can be used in many devices, including, but not limitedto, wings, canards, horizontal and vertical stabilizers, rotor bladesfor propellers, fans, compressors, turbines, helicopter blades, andstator vanes for compressors and turbines. The capability to alter theaerodynamic performance of a device by altering its shape (e.g., the“camber” of an airfoil) during various phases of operation can lead tosignificant performance improvements.

In operation, airfoil 1102 creates a pressure difference from a suctionsurface on one side of airfoil 1102 to a pressure surface on an oppositeside by imposing on the fluid flow a greater curvature on the suctionsurface than on the pressure surface. A reduction of the efficacy ofairfoil results 1102, however, when the fluid flow boundary layerseparates from the suction surface. One strategy for reducing thetendency toward boundary layer separation is to inject fluid into theboundary layer through jets in the suction surface. Typically, theeffectiveness of this strategy increases as the velocity of the injectedfluid approaches the velocity of the bulk fluid flow.

FIG. 11 depicts plasma jet 802 embedded flush with an external surface1104 of airfoil 1102. The position of one or more plasma jets 802 alongairfoil surface 1104 can be determined based on the particular effect onthe freestream fluid F desired. Airfoil 1102 is shown at zero degreeswith respect to fluid F, also referred to as zero degrees angle ofattack, however, plasma jets 802 can also function at other angles ofattack. For example, at higher angles of attack, the separationperformance of wing 1004 can be controlled and/or tailored byappropriate placement and operation of plasma jets 802. Note that plasmajets 802 can be oriented to inject fluid at any desired angle relativeto fluid F.

FIG. 12 shows plasma jet 802 in operation forming a pulsed jet flow intothe freestream fluid F. When plasma jet 802 is a zero net mass flow jet,a closed recirculating flow region 1202 is formed, effectively modifyingthe aerodynamic shape of airfoil surface 1202. The freestream fluid Fflows over the recirculating region 1202 just as if recirculating flowregion 1202 were a solid part of airfoil surface 1202. Thus, theaerodynamic characteristics of airfoil 1102 can be changed by operationof plasma jet 802.

FIGS. 11 and 12 show a single plasma jet 802, however, an array ofplasma jets 802 are shown in wing 1004. Other arrangements of plasmajets 802 are possible, for example, plasma jets 802 can be configured ina two-dimensional array, as well as in the lower and/or upper skin ofwing 1004. Multiple plasma jets 802 can be individually addressable, andall, or only a select portion, of plasma jets 802 may be activated atone time. In this manner, the apparent aerodynamic shape of the wing1004 may be specifically tailored for a given flight regime. If wing1004 is configured with pressure, or other appropriate sensors, then acontrol computer can evaluate the forces on the wing during flight anddetermine the appropriate plasma jets 802 to activate in order tooptimally tailor the effective aerodynamic shape of airfoil 1102.

It is anticipated that plasma jets 802 can also be used on leadingand/or trailing edges of various portions of an aircraft or otherdevice, in addition to, or instead of, conventional control surfaces,such as rudders, ailerons, flaps, elevators, among others, to controlthe attitude and position of the device in which plasma jets 802 areinstalled. For example, on an aircraft, arrays of plasma jets 802 can bepositioned in both wings and operated to create higher lift on one sideof the center of gravity of the aircraft than on the other. Theasymmetrical lifting force will cause a rolling moment, similar to theeffect of aileron deflections in a conventional aircraft. One advantageof plasma jets 802 over conventional control surfaces is the absence ofhinge lines, which have a higher RADAR cross-section than plasma jets802. Accordingly, a device that incorporates plasma jets 802 instead ofconventional hinged control surfaces will be less observable with RADARsensors.

More aft locations can also be used with plasma jets 802 pointing moredirectly downstream to increase lift through pressure reduction,increase L/D, delay separation and thereby increase the maximumattainable lift (C_(Lmax)), and even provide primary thrust for someapplications. Differential application of plasma jets 802 can also beused to provide pitch, roll, and yaw control. Plasma jets 802 can alsobe used near leading and/or trailing edges to replace the conventionalcontrol surfaces.

In addition to the aerodynamic forces, acceleration or deceleration ofthe air flowing around an aircraft creates a direct thrust (or drag)force on the aircraft. The moment added to the air stream by plasma jets802 can create a reaction force on the aircraft. This force can be asignificant thrust on the vehicle, which can be applied symmetrically,or asymmetrically to provide additional control moments.

Referring now to FIG. 13, a perspective view of an embodiment ofself-propelled rotor 1300 is shown comprising an airfoil 1310, a firstpulse detonation actuator 1320, and a hub 1330. Hub 1330 is coupled toairfoil 1310 and transmits force between an external shaft (not shown)and airfoil 1310 to rotate airfoil 1310. Fluid flow over the surface ofairfoil 1310 generates a lift force. One or more pulse detonationactuators 1320 can be disposed inside airfoil 1310 and configured todetonate a fuel/air mixture to produce a pressure rise and velocityincrease of combustion products inside pulse detonation actuator 1320.To modulate the lift force, airfoil 1310 has a plurality of lift controlholes 1340 for communicating combustion product flows from pulsedetonation actuators 1320 to the surface of airfoil 1320. To impart athrust force to airfoil 1310 and thus a torque about an axis of hub1330, first pulse detonation actuator 1320 comprises an exhaust nozzle1350 for directing the combustion products overboard. Apparatus 1300 isthus a self-propelled rotor useful, for example, as a helicopter rotor.In some embodiments, exhaust nozzle 1350 is absent so that apparatus1300 is a passive rotor useful, for example, in a turbine or compressorof a gas turbine engine. In other embodiments, hub 1330 is absent sothat airfoil 1310 is useful, for example, as an aircraft wing orhelicopter rotor blade.

The term “pulse detonation actuator” (PDA) refers to any device orsystem which produces both a pressure rise and velocity increase from aseries of repeating detonations or quasi-detonations within the device.A “quasi-detonation” refers to a combustion process which produces apressure rise and velocity increase higher than the pressure rise andvelocity increase produced by a deflagration wave. Typical embodimentsof PDAs 1320 comprise a means of impulsively igniting a fuel/airmixture, and a detonation chamber in which pressure wave frontsinitiated by the ignition process coalesce to produce a detonation wave.The geometry of the detonation chamber is such that the pressure rise ofthe detonation wave expels combustion products out exhaust nozzle 1350.As used herein, “impulsively detonating” refers to a process ofrepeating detonations or quasi-detonations wherein each detonation orquasi-detonation is initiated either by external ignition (for example,spark discharge or laser pulse) or by gas dynamic processes (forexample, shock initiation or autoignition).

One way to achieve a higher exhaust velocity is to increase the speed atwhich the fuel is burnt. The speed is increased by introducingturbulence and enhanced mixing in PDAs 1320. Plasma jets 802 can beincluded in PDAs 1320 to improve the fuel-air mixture for bettercombustion and introduce turbulence to increase flame speed.

Lift control holes 1340 are shaped and oriented to promote attachment ofthe boundary layer to the surface of airfoil 1310 so that the lift forceis an increasing function of the combustion product flows. In analternative embodiment, lift control holes 1340 are shaped to promoteseparation of the boundary layer from the surface of airfoil 1310 sothat the lift force is a decreasing function of the combustion productflows.

In some embodiments, one or more PDAs 1320 can operate out of phase withother PDAs 1320. Out of phase operation raises the frequency with whichcombustion product pulses are delivered to the boundary layer and, insome applications, produces a temporally more uniform boundary layercompared to operation with a single PDA 1320.

Plasma jets 802 can also be used to cool heat-producing bodies, which isa concern in many different technologies, such as integrated circuits insingle- and multi-chip modules (MCMs). Additionally, either zero netmass flow plasma jets 802, and/or open cavity plasma jets 200 such asshown in FIG. 2B can be implemented for any desired application, basedon the mass flow available and other design considerations.

While the present disclosure describes various embodiments, theseembodiments are to be understood as illustrative and do not limit theclaim scope. Many variations, modifications, additions and improvementsof the described embodiments are possible. For example, those havingordinary skill in the art will readily implement the processes necessaryto provide the structures and methods disclosed herein. Variations andmodifications of the embodiments disclosed herein may also be made whileremaining within the scope of the following claims. For example, housing109 can be formed by any suitable type of enclosure formed inindependent structure as well as enclosures formed by surroundingstructure(s). Additionally, any suitable component or combination ofcomponents can be used for controller 102, plasma generator 104, andelectromagnetic accelerator 106 in any embodiments of plasma systems,such as systems 100 (FIG. 1), 200 (FIG. 2A), 300 (FIG. 3A), and 400(FIG. 4), among others. The functionality and combinations offunctionality of the individual modules can be reconfigured to provideany appropriate functionality. In the claims, unless otherwise indicatedthe article “a” is to refer to “one or more than one”.

1. A plasma jet system, comprising: a housing including one opening,wherein a partially ionized fluid is drawn into the opening; anelectromagnetic accelerator configured to generate an electric fieldthat accelerates the ionized fluid in the housing toward the opening inthe housing, and to generate a magnetic field transverse to the electricfield; a controller coupled to modulate the electromagnetic accelerator,thereby causing the ionized fluid to form a pulsed plasma flow throughthe opening in the housing; and a conductor configured to transportelectrons to a location where the electrons collected in the enclosureare reinserted into the plasma flow.
 2. The plasma jet system of claim1, wherein the housing includes an electron beam window through whichelectron beams are supplied to further ionize the fluid in the housing.3. The plasma jet system of claim 1, wherein the electromagneticaccelerator comprises a series of electrodes coupled to the housing, andthe controller is operable to modulate electrical current to theelectrodes to control an electric field generated by the electrodes. 4.The plasma jet system of claim 1, further comprising a structure,wherein the housing is configured in a structure so that the plasma flowmixes with a secondary fluid in the structure.
 5. The plasma jet systemof claim 1, further comprising: a nozzle, wherein the housing isconfigured in the nozzle so that the plasma flow varies an effectivethroat area of the nozzle.
 6. The plasma jet system of claim 1, furthercomprising: a nozzle, wherein the housing is configured in the nozzle sothat the plasma flow vectors the direction of thrust exiting the nozzle.7. The plasma jet system of claim 1, further comprising: an aerodynamicstructure, wherein the housing is configured in the aerodynamicstructure so that the plasma flow changes at least a portion of theeffective shape of the aerodynamic structure.
 8. The plasma jet systemof claim 1, further comprising: an aerodynamic structure, wherein thehousing is configured in the aerodynamic structure so that the plasmaflow affects the pressure on the aerodynamic surface by accelerating ordecelerating the plasma flow.
 9. The plasma jet system of claim 1,further comprising: an aerodynamic structure, wherein the housing isconfigured in the aerodynamic structure so that the plasma flow createsforces and moments on the aerodynamic structure in reaction to theacceleration or deceleration of the plasma flow.
 10. The plasma jetsystem of claim 9, wherein the aerodynamic structure comprises at leastone of the group consisting of: an aircraft wing and an aircraft controlsurface.
 11. The plasma jet system of claim 1, wherein the housing isconfigured in a structure so that the plasma flow cools at least aportion of the structure.
 12. The plasma jet system of claim 1, whereinthe structure is a pulse detonation actuator, and the plasma flow mixesa fuel-air mixture in the pulse detonation actuator.
 13. A methodcomprising: accelerating an ionized fluid through an electric field in ahousing, wherein the housing includes one opening and the electric fieldis oriented to accelerate the ionized fluid in the direction of theopening, thereby forming a plasma flow; generating a magnetic fieldtransverse to the electric field, wherein the magnetic field decelerateselectrons in the housing; collecting decelerated electrons; andtransporting collected electrons to a location where the collectedelectrons are reinserted into the plasma flow.
 14. The method of claim13 further comprising: pulsing the electric field at a predeterminedfrequency, thereby forming vortex rings of the plasma flow as the plasmaflow exits the housing.
 15. The method of claim 13 further comprising:injecting electron beams into the housing to generate the plasma. 16.The method of claim 13, further comprising: injecting the plasma flowinto a primary flow to alter the direction of the primary flow.
 17. Themethod of claim 13, further comprising: using the plasma flow to performat least one of the group consisting of: altering the aerodynamiccharacteristics of a surface; controlling aerodynamic forces and momentsacting on a device in which the housing is installed; mixing fuel andair in a device in which the housing is installed; and controllingaerodynamic forces and moments acting on a device in which the housingis installed.
 18. An apparatus comprising: an enclosure including oneopening; an electric field generator operable to generate an electricfield in the enclosure; a magnetic field generator operable to generatea magnetic field transverse to the electric field; an ionized fluidsource configured to provide ionized fluid in the enclosure, wherein theelectric field is oriented to accelerate the ionized fluid toward theopening to generate a plasma jet; and a conductor configured totransport the electrons to a location where electrons collected in theenclosure are reinserted into the plasma flow.
 19. The apparatus ofclaim 18 further comprising: a controller operable to control at leastone of the group consisting of: the electric field generator to providea pulsed electric field; the strength of the electric field generated bythe electric field generator; the ionized fluid source; sequentiallyactivate and deactivate a series of pairs of electrodes of oppositepolarity; and the strength of the electric field generated by theelectric field generator.